Recent advances in self-adjuvanting glycoconjugate vaccines

Intranasal Self-Adjuvanted Lipopeptide Vaccines Elicit High Antibody Titers and Strong Cellular Responses against SARS-CoV-2

Despite concerted efforts to tackle the COVID-19 pandemic, the persistent transmission of SARS-CoV-2 demands continued research into novel vaccination strategies to combat the virus. In light of this, intranasally administered peptide vaccines, particularly those conjugated to an immune adjuvant to afford so-called "self-adjuvanted vaccines", remain underexplored. Here, we describe the synthesis and immunological evaluation of self-adjuvanting peptide vaccines derived from epitopes of the spike glycoprotein of SARS-CoV-2 covalently fused to the potent adjuvant, Pam2Cys, that targets toll-like receptor 2 (TLR2). When administered intranasally, these vaccines elicited a strong antigen-specific CD4+ and CD8+ T-cell response in the lungs as well as high titers of IgG and IgA specific to the native spike protein of SARS-CoV-2. Unfortunately, serum and lung fluid from mice immunized with these vaccines failed to inhibit viral entry in spike-expressing pseudovirus assays. Following this, we designed and synthesized fusion vaccines composed of the T-cell epitope discovered in this work, covalently fused to epitopes of the receptor-binding domain of the spike protein reported to be neutralizing. While antibodies elicited against these fusion vaccines were not neutralizing, the T-cell epitope retained its ability to stimulate strong antigen-specific CD4+ lymphocyte responses within the lungs. Given the Spike(883-909) region is still completely conserved in SARS-CoV-2 variants of concern and variants of interest, we envision the self-adjuvanting vaccine platform reported here may inform future vaccine efforts.

Unveiling the potential role of micro/nano biomaterials in the treatment of Helicobacter pylori infection

INTRODUCTION

Helicobacter pylori causes stubborn infections and leads to a variety of stomach disorders, such as peptic ulcer, chronic atrophic gastritis, and gastric cancer. Although antibiotic-based approaches have been widely used against H. pylori, some challenges such as antibiotic resistance are increasing in severity. Therefore, simpler but more effective strategies are needed.

AREAS COVERED

In this review, basic information on functionalized and non-functionalized micro/nano biomaterials and routes of administration for H. pylori inhibition are provided in an easy-to-understand format. Afterward, in vitro and in vivo studies of some promising bio-platforms including metal-based biomaterials, biopolymers, small-molecule saccharides, and vaccines for H. pylori inhibition are discussed in a holistic manner.

EXPERT OPINION

Functionalized or non-functionalized micro/nano biomaterials loaded with anti-H. pylori agents can show efficient bactericidal activity with no/slight negative influence on the host gastrointestinal microbiota. However, this claim needs to be substantiated with hard data such as assessment of the biopharmaceutical parameters of anti-H. pylori systems and the measurement of diversity/abundance of bacterial genera in the host gastric/gut microbiota before and after H. pylori eradication.

Glycoconjugates: Advances in modern medicines and human health

Glycans and their glycoconjugates are complex biomolecules that are crucial for various biological processes. Glycoconjugates are found in all domains of life. They are covalently linked to key biomolecules such as proteins and lipids to play a pivotal role in cell signaling, adhesion, and recognition. The diversity of glycan structures and the associated complexity of glycoconjugates is the reason for their role in intricate biosynthetic pathways. Glycoconjugates play an important role in various diseases where they are actively involved in the immune response as well as in the pathogenicity of infectious diseases. In addition, various autoimmune diseases have been linked to glycosylation defects of different biomolecules, making them an important molecule in the field of medicine. The glycoconjugates have been explored for the development of therapeutics and vaccines, representing a breakthrough in medical science. They also hold significance in research studies to understand the mechanisms behind various biological processes. Finally, glycoconjugates have found an emerging role in various industrial and environmental applications which have been discussed here.

The synthesis and preliminary immunological evaluation of a dual-adjuvant SARS-CoV-2 RBD vaccine: Covalent integration of TLR7/8 and iNKT cell agonists

Covalently linking an adjuvant to an antigenic protein enhances its immunogenicity by ensuring a synergistic delivery to the immune system, fostering a more robust and targeted immune response. Most adjuvant-protein conjugate vaccines incorporate only one adjuvant due to the difficulties in its synthesis. However, there is a growing interest in developing vaccines with multiple adjuvants designed to elicit a more robust and targeted immune response by engaging different aspects of the immune system for complex diseases where traditional vaccines fall short. Here, we pioneer the synthesis of a dual-adjuvants protein conjugate Vaccine 1 by assembling a toll-like receptor 7/8 (TLR7/8) agonist, an invariant natural killer T cell (iNKT) agonist with a clickable bicyclononyne (BCN). The BCN group can bio-orthogonally react with azide-modified severe acute respiratory syndrome coronavirus-2 receptor-binding domain (SARS-CoV-2 RBD) trimer antigen to give the three-component Vaccine 1. Notably, with a mere 3 μg antigen, it elicited a balanced subclass of IgG titers and 20-fold more IgG2a than control vaccines, highlighting its potential for enhancing antibody-dependent cellular cytotoxicity. This strategy provides a practicable way to synthesize covalently linked dual immunostimulants. It expands the fully synthetic self-adjuvant protein vaccine that uses a single adjuvant to include two different types of adjuvants.

Synthesis and immunological evaluation of TLR1/2 ligand-conjugated RBDs as self-adjuvanting vaccine candidates against SARS-CoV-2

We synthesized and evaluated Pam3CSK4-conjugated receptor binding domain (RBD)/deglycosylated RBD as potential anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine candidates. Our investigation revealed the critical importance of limiting the number of introduced Pam3CSK4 molecules to the RBD in order to preserve its antigenicity. We also confirmed the harmonious integration of the adjuvant-conjugation strategy with the glycan-shield removal strategy.

Merging Solid-Phase Peptide Synthesis and Automated Glycan Assembly to Prepare Lipid-Peptide-Glycan Chimeras

Biomaterials with improved biological features can be obtained by conjugating glycans to nanostructured peptides. Creating peptide-glycan chimeras requires superb chemoselectivity. We expedite access to such chimeras by merging peptide and glycan solid-phase syntheses employing a bifunctional monosaccharide. The concept was explored in the context of the on-resin generation of a model α(1→6)tetramannoside linked to peptides, lipids, steroids, and adamantane. Chimeras containing a β(1→6)tetraglucoside and self-assembling peptides such as FF, FFKLVFF, and the amphiphile palmitoyl-VVVAAAKKK were prepared in a fully automated manner. The robust synthetic protocol requires a single purification step to obtain overall yields of about 20 %. The β(1→6)tetraglucoside FFKLVFF chimera produces micelles rather than nanofibers formed by the peptide alone as judged by microscopy and circular dichroism. The peptide amphiphile-glycan chimera forms a disperse fiber network, creating opportunities for new glycan-based nanomaterials.

Development of synthetic, self-adjuvanting, and self-assembling anticancer vaccines based on a minimal saponin adjuvant and the tumor-associated MUC1 antigen

The overexpression of aberrantly glycosylated tumor-associated mucin-1 (TA-MUC1) in human cancers makes it a major target for the development of anticancer vaccines derived from synthetic MUC1-(glyco)peptide antigens. However, glycopeptide-based subunit vaccines are weakly immunogenic, requiring adjuvants and/or additional immunopotentiating approaches to generate optimal immune responses. Among these strategies, unimolecular self-adjuvanting vaccine constructs that do not need coadministration of adjuvants or conjugation to carrier proteins emerge as a promising but still underexploited approach. Herein, we report the design, synthesis, immune-evaluation in mice, and NMR studies of new, self-adjuvanting and self-assembling vaccines based on our QS-21-derived minimal adjuvant platform covalently linked to TA-MUC1-(glyco)peptide antigens and a peptide helper T-cell epitope. We have developed a modular, chemoselective strategy that harnesses two distal attachment points on the saponin adjuvant to conjugate the respective components in unprotected form and high yields via orthogonal ligations. In mice, only tri-component candidates but not unconjugated or di-component combinations induced significant TA-MUC1-specific IgG antibodies able to recognize the TA-MUC1 on cancer cells. NMR studies revealed the formation of self-assembled aggregates, in which the more hydrophilic TA-MUC1 moiety gets exposed to the solvent, favoring B-cell recognition. While dilution of the di-component saponin-(Tn)MUC1 constructs resulted in partial aggregate disruption, this was not observed for the more stably-organized tri-component candidates. This higher structural stability in solution correlates with their increased immunogenicity and suggests a longer half-life of the construct in physiological media, which together with the enhanced antigen multivalent presentation enabled by the particulate self-assembly, points to this self-adjuvanting tri-component vaccine as a promising synthetic candidate for further development.

Site-Specific Multi-Functionalization of the Carrier Protein CRM197 by Disulfide Rebridging for Conjugate Vaccine Development

Conjugation of an antigen to a carrier protein is widely used for vaccine development. To develop the next generation of conjugate vaccines, we describe here a method for the controlled multi-functionalization of the widely employed carrier protein CRM197 with a carbohydrate-based antigen and an immune potentiator. The approach is based on the selective reduction of one of the disulfides of CRM197 followed by disulfide rebridging employing an appropriately functionalized dibromopyridazinedione. Efficient protein modification required that the reduction and functionalization with a dibromopyridazinedione was performed as a one-step procedure with control over the reaction temperature. Furthermore, ligations were most successful when dibromopyridazinediones were employed having a functional entity such as a TLR7/8 agonist and a cyclooctyne for further modification. Site-specific conjugation avoids modification of T-epitopes of the carrier protein and covalent attachment of an immune potentiator will ensure that cytokines are produced where the vaccine interacts with relevant immune cells resulting in efficient immune potentiation.

Recent advances and future perspectives on carbohydrate-based cancer vaccines and therapeutics

Carbohydrates are abundantly expressed on the surface of both eukaryotic and prokaryotic cells, often as post translational modifications of proteins. Glycoproteins are recognized by the immune system and can trigger both innate and humoral responses. This feature has been harnessed to generate vaccines against polysaccharide-encapsulated bacteria such as Streptococcus pneumoniae, Hemophilus influenzae type b and Neisseria meningitidis. In cancer, glycosylation plays a pivotal role in malignancy development and progression. Since glycans are specifically expressed on the surface of tumor cells, they have been targeted for the discovery of anticancer preventive and therapeutic treatments, such as vaccines and monoclonal antibodies. Despite the various efforts made over the last years, resulting in a series of clinical studies, attempts of vaccination with carbohydrate-based candidates have proven unsuccessful, primarily due to the immune tolerance often associated with these glycans. New strategies are thus deployed to enhance carbohydrate-based cancer vaccines. Moreover, lessons learned from glycan immunobiology paved the way to the development of new monoclonal antibodies specifically designed to recognize cancer-bound carbohydrates and induce tumor cell killing. Herein we provide an overview of the immunological principles behind the immune response towards glycans and glycoconjugates and the approaches exploited at both preclinical and clinical level to target cancer-associated glycans for the development of vaccines and therapeutic monoclonal antibodies. We also discuss gaps and opportunities to successfully advance glycan-directed cancer therapies, which could provide patients with innovative and effective treatments.

MPLA-Adjuvanted Liposomes Encapsulating S-Trimer or RBD or S1, but Not S-ECD, Elicit Robust Neutralization Against SARS-CoV-2 and Variants of Concern

Safe and effective vaccines are the best method to defeat worldwide SARS-CoV-2 and its circulating variants. The SARS-CoV-2 S protein and its subunits are the most attractive targets for the development of protein-based vaccines. In this study, we evaluated three lipophilic adjuvants, monophosphoryl lipid A (MPLA), Toll-like receptor (TLR) 1/2 ligand Pam3CSK4, and α-galactosylceramide (α-GalCer), in liposomal and nonliposomal vaccines. The immunological results showed that the MPLA-adjuvanted liposomal vaccine induced the strongest humoral and cellular immunity. Therefore, we further performed a systematic comparison of S-trimer, S-ECD, S1, and RBD as antigens in MPLA-adjuvanted liposomes and found that, although these four vaccines all induced robust specific antibody responses, only S-trimer, S1, and RBD liposomes, but not S-ECD, elicited potent neutralizing antibody responses. Moreover, RBD, S-trimer, and S1 liposomes effectively neutralized variants (B.1.1.7/alpha, B.1.351/beta, P.1/gamma, B.1.617.2/delta, and B.1.1.529/omicron). These results provide important information for the subunit vaccine design against SARS-CoV-2 and its variants.

Lipid-Based Nanoparticles in the Clinic and Clinical Trials: From Cancer Nanomedicine to COVID-19 Vaccines

COVID-19 vaccines have been developed with unprecedented speed which would not have been possible without decades of fundamental research on delivery nanotechnology. Lipid-based nanoparticles have played a pivotal role in the successes of COVID-19 vaccines and many other nanomedicines, such as Doxil® and Onpattro®, and have therefore been considered as the frontrunner in nanoscale drug delivery systems. In this review, we aim to highlight the progress in the development of these lipid nanoparticles for various applications, ranging from cancer nanomedicines to COVID-19 vaccines. The lipid-based nanoparticles discussed in this review are liposomes, niosomes, transfersomes, solid lipid nanoparticles, and nanostructured lipid carriers. We particularly focus on the innovations that have obtained regulatory approval or that are in clinical trials. We also discuss the physicochemical properties required for specific applications, highlight the differences in requirements for the delivery of different cargos, and introduce current challenges that need further development. This review serves as a useful guideline for designing new lipid nanoparticles for both preventative and therapeutic vaccines including immunotherapies.